linux-kernel - RE: [PATCH 02/11] PCI: Cleanup pci_rebar_bytes_to

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Message-ID: <IA1PR11MB64183AD6FDE18C9DF0014282C109A@IA1PR11MB6418.namprd11.prod.outlook.com>
Date: Thu, 11 Sep 2025 17:25:16 +0000
From: "Ruhl, Michael J" <michael.j.ruhl@...el.com>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>, Bjorn Helgaas
	<bhelgaas@...gle.com>, Krzysztof Wilczyński
	<kw@...ux.com>, Christian König
	<christian.koenig@....com>, "Winiarski, Michal" <michal.winiarski@...el.com>,
	Alex Deucher <alexander.deucher@....com>, "amd-gfx@...ts.freedesktop.org"
	<amd-gfx@...ts.freedesktop.org>, David Airlie <airlied@...il.com>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
	"intel-xe@...ts.freedesktop.org" <intel-xe@...ts.freedesktop.org>, "Jani
 Nikula" <jani.nikula@...ux.intel.com>, Joonas Lahtinen
	<joonas.lahtinen@...ux.intel.com>, "De Marchi, Lucas"
	<lucas.demarchi@...el.com>, "Vivi, Rodrigo" <rodrigo.vivi@...el.com>, "Simona
 Vetter" <simona@...ll.ch>, Tvrtko Ursulin <tursulin@...ulin.net>,
	?UTF-8?q?Thomas=20Hellstr=C3=B6m?= <thomas.hellstrom@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC: "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: RE: [PATCH 02/11] PCI: Cleanup pci_rebar_bytes_to_size() and move
 into rebar.c

>-----Original Message-----
>From: dri-devel <dri-devel-bounces@...ts.freedesktop.org> On Behalf Of Ilpo
>Järvinen
>Sent: Thursday, September 11, 2025 3:56 AM
>To: linux-pci@...r.kernel.org; Bjorn Helgaas <bhelgaas@...gle.com>;
>Krzysztof Wilczyński <kw@...ux.com>; Christian König
><christian.koenig@....com>; Winiarski, Michal <michal.winiarski@...el.com>;
>Alex Deucher <alexander.deucher@....com>; amd-gfx@...ts.freedesktop.org;
>David Airlie <airlied@...il.com>; dri-devel@...ts.freedesktop.org; intel-
>gfx@...ts.freedesktop.org; intel-xe@...ts.freedesktop.org; Jani Nikula
><jani.nikula@...ux.intel.com>; Joonas Lahtinen
><joonas.lahtinen@...ux.intel.com>; De Marchi, Lucas
><lucas.demarchi@...el.com>; Vivi, Rodrigo <rodrigo.vivi@...el.com>; Simona
>Vetter <simona@...ll.ch>; Tvrtko Ursulin <tursulin@...ulin.net>; ?UTF-
>8?q?Thomas=20Hellstr=C3=B6m?= <thomas.hellstrom@...ux.intel.com>; linux-
>kernel@...r.kernel.org
>Cc: linux-doc@...r.kernel.org; Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
>Subject: [PATCH 02/11] PCI: Cleanup pci_rebar_bytes_to_size() and move into
>rebar.c
>
>Move pci_rebar_bytes_to_size() from include/linux/pci.h into rebar.c as
>it does not look very trivial and is not expected to be performance
>critical.
>
>Convert literals to use a newly added PCI_REBAR_MIN_SIZE define.
>
>Also add kernel doc for the function as the function is exported.
>
>Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
>---
> drivers/pci/rebar.c | 23 +++++++++++++++++++++++
> include/linux/pci.h | 10 +++-------
> 2 files changed, 26 insertions(+), 7 deletions(-)
>
>diff --git a/drivers/pci/rebar.c b/drivers/pci/rebar.c
>index b87cfa6fb3ef..961bd43be02b 100644
>--- a/drivers/pci/rebar.c
>+++ b/drivers/pci/rebar.c
>@@ -7,11 +7,34 @@
> #include <linux/errno.h>
> #include <linux/export.h>
> #include <linux/ioport.h>
>+#include <linux/log2.h>
> #include <linux/pci.h>
>+#include <linux/sizes.h>
> #include <linux/types.h>
>
> #include "pci.h"
>
>+#define PCI_REBAR_MIN_SIZE	((resource_size_t)SZ_1M)
>+
>+/**
>+ * pci_rebar_bytes_to_size - Convert size in bytes to PCI BAR Size
>+ * @bytes: size in bytes
>+ *
>+ * Convert bytes to BAR Size in Resizable BAR Capability (PCIe r6.2,
>+ * sec. 7.8.6.3).
>+ *
>+ * Return: BAR Size as defined in the PCIe spec (0=1MB, bit 31=128TB).

Thank you for this helper and documentation.  I wasted a lot of time to trying to understand
this usage a few years ago.

Regardless of the rest of the patch set, this update should be used.

Reviewed-by: Michael J. Ruhl <mjruhl@...ana.ai

Mike

>+ */
>+int pci_rebar_bytes_to_size(u64 bytes)
>+{
>+	int rebar_minsize = ilog2(PCI_REBAR_MIN_SIZE);
>+
>+	bytes = roundup_pow_of_two(bytes);
>+
>+	return max(ilog2(bytes), rebar_minsize) - rebar_minsize;
>+}
>+EXPORT_SYMBOL_GPL(pci_rebar_bytes_to_size);
>+
> void pci_rebar_init(struct pci_dev *pdev)
> {
> 	pdev->rebar_cap = pci_find_ext_capability(pdev,
>PCI_EXT_CAP_ID_REBAR);
>diff --git a/include/linux/pci.h b/include/linux/pci.h
>index 59876de13860..894e9020b07d 100644
>--- a/include/linux/pci.h
>+++ b/include/linux/pci.h
>@@ -1418,16 +1418,12 @@ void pcibios_reset_secondary_bus(struct pci_dev
>*dev);
> void pci_update_resource(struct pci_dev *dev, int resno);
> int __must_check pci_assign_resource(struct pci_dev *dev, int i);
> void pci_release_resource(struct pci_dev *dev, int resno);
>-static inline int pci_rebar_bytes_to_size(u64 bytes)
>-{
>-	bytes = roundup_pow_of_two(bytes);
>-
>-	/* Return BAR size as defined in the resizable BAR specification */
>-	return max(ilog2(bytes), 20) - 20;
>-}
>
>+/* Resizable BAR related routines */
>+int pci_rebar_bytes_to_size(u64 bytes);
> u32 pci_rebar_get_possible_sizes(struct pci_dev *pdev, int bar);
> int __must_check pci_resize_resource(struct pci_dev *dev, int i, int size);
>+
> int pci_select_bars(struct pci_dev *dev, unsigned long flags);
> bool pci_device_is_present(struct pci_dev *pdev);
> void pci_ignore_hotplug(struct pci_dev *dev);
>--
>2.39.5